This invention relates to a method for enhancing areas of interest in an image composed of a plurality of digital values, and more particularly to a method for displaying a visually enhanced radiograph by mapping the enhanced plurality of digital values onto a gray scale transfer (GST) function of a display medium.
There exists significant activity in the development of digital x-ray image data capture systems. In such systems direct conversion to an electrical signal of the incident radiation is obtained using a plurality of sensors (also known as pixels) in an array. The sensor output is almost invariably immediately converted to a digital signal by an analog-to-digital converted as known in the art and further processed and stored in a databank for use in the eventual display of the data as a radiograph. U.S. Pat. No. 5,313,066 issued to Lee et al. (hereinafter the ""066 patent) and U.S. Pat. No. 5,315,101 issued to Hughes et al. describe typical such sensor arrays and their contents are incorporated herein by reference. Even though several different technologies are being utilized, the output data are quite similar.
A major advantage of digital data detection systems is the wide dynamic range of signal capture. Display media, such as radiographic film or cathode ray tube (CRT) displays, on the other hand, have a substantially more limited dynamic range. A typical digital x-ray capture system can have a useful dynamic detection range of greater than a 1,000:1. However, the useful image data are generally limited to a dynamic range of less than 100:1. There is, therefore, need to determine and select the optimal limited range of useful data for diagnostic display, and then properly display such range on the available display medium.
This problem, which reduces to a need for a method whereby the exposure sensor output is mapped onto the density transfer function of the display device, has been addressed by the art in numerous ways. Typically the sensor output is digitized, and a histogram of the frequency of occurrence of digital values representing detected exposure is constructed. Following construction of the histogram, cutoff points eliminating values under selected minimum occurrence for both ends of the scale are determined and the digital values in the remaining range are mapped onto the display transfer function, usually using a look-up table (LUT), as is well known in the art. These steps are rather fundamental and intuitive. What is significant and the subject of continuing research is the manner in which the density values are processed and mapped on the transfer function to create an optimal radiograph wherein the features of interest are distinguishable from background features.
U.S. Pat. No. 5,164,993 issued Nov. 17, 1992 to Capozzi et al. together with U.S. Pat. No. 5,046,118 issued to Ajewole et al. and U.S. Pat. No. 4,868,651 issued to Chou et al., are believed to represent the current state of the art in explaining and solving the problems associated with such displays. A method for automatically identifying the range of useful digital values to be used for diagnostic display, and to provide an appropriate gray scale transfer (GST) function to optimize the diagnostic value of the final displayed image, either hard or soft copy, is described in PCT International Publication Number WO 98/37738 to Schwenker et al., and incorporated herein by reference.
Other methods are known in the art for processing matrices of digital values to provide better contrast. For example, a technique known as xe2x80x9cunsharp maskingxe2x80x9d essentially comprises taking the original matrix of digital values, creating a xe2x80x9csmoothedxe2x80x9d matrix of digital values from the original matrix, and adding back the smoothed matrix to the original matrix. Creating a xe2x80x9csmoothedxe2x80x9d matrix entails creating a new value for each data point that is an average of a number of adjacent data points in a specified filter range. Thus, for example, a bxc3x97b smoothing filter is used where n is an odd number much less than the size of the total image matrix. The average or weighted average of each bxc3x97b matrix is used to calculate a replacement value for the central location in the bxc3x97b matrix.
The application of digital x-ray technology allows the processing of the digital image in ways that were heretofore unavailable with image acquisition directly onto film. In a typical x-ray, there may be many features of interest covering a broad range of anatomy of the patient. This broad range may include areas of anatomy having vastly disparate radiation absorption properties. As a result, an area of anatomy having relatively low radiation absorption may be relatively light on the radiograph, while an area having relatively high radiation absorption may be relatively dark. Using a typical non-digital x-ray system, multiple images at multiple radiation doses are typically created so that the features in each area can be distinguished. Some digital x-ray systems have addressed this problem using localized histogram equalization methods, simple dynamic range compression, or enhanced visualization processing.
Other methods are still desired, however, which do not compromise the contrast of the resulting image. It is thus an object of the present invention to provide a method that allows visualization of a broad range of anatomy on a single image without requiring manipulation to view light or dark areas.
The present invention comprises a method for displaying on a display medium an image corresponding to detected exposures to radiation of a plurality of sensors in an array, the detected exposures converted to a starting matrix having n rows and m columns of digital values with each digital value representing an optical density. The method comprises the steps of creating a weighted, smoothed, subtracted matrix, adding the weighted, smoothed, subtracted matrix to the starting matrix to create an enhanced matrix, and using the digital values from the enhanced matrix to display an image.
The invention also comprises a program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform the method steps. A digital x-ray image data capture system may comprise such a program storage device as well as a source of penetrative radiation for emitting an unmodulated radiation beam along a path and a plurality of sensors in an array of n rows and m columns positioned in the beam path. The plurality of sensors is adapted for receiving and detecting exposure to at least a modulated radiation beam derived from the unmodulated radiation beam. Each sensor is adapted to produce a sensor output proportional to the detected exposure. An analog-to-digital converter adapted to receive the sensor output, convert the sensor output to a digital value, and transmit the digital value to the program storage device is also included in the system.
The digital x-ray image data capture system may be used for carrying out a method of providing a radiographic visualization of a portion of anatomy, the method comprising placing the portion of anatomy in the path of the unmodulated radiation beam between the source and the array of sensors. The unmodulated radiation beam is modulated into a modulated beam as the beam penetrates the portion of anatomy, and then the exposure of the sensors to the modulated beam is detected.